The Circum Pacific Belt is the most active ring of earthquake activity on the planet. It is located on the west coast of the Americas (North and South) and Asia. The illustration above shows the geologic actions ocuring when a oceanic crust pushes into a continental crust. Being more dense, the oceanic crust tends to 'sink', or be subducted beneath the lighter density continental crust. This process is slow, since plates typically move at a rate of only a few centimeters per year, but their mass is considerable, and the resulting force from a plate to plate collision is huge. It fractures rock formations, causing faults, creates earthquakes and can even result in the eruption of volcanos. The mass of the earth has been pretty much the same for billions of years, with the only additions coming from outer space, in the form of metorites or asteroids striking the surface. These occurances are very rare, and have contributed very little (probably) to the mass of the earth, percentage wise. So, when mass from the upper crusts gets assimilated down into the mantle and lower layers of the planet, some mass must be displaced, in the form of mountains, or volcanic lava flow to the surface. mass can not be created or destroyed, only changed in form, physics teaches us, so everything will balance somehow.

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